"The police met a couple of people leaving" the garden, said Walker spokesperson Ryan French. However, the Walker didn't realize that the sculpture had been vandalized until dawn on Saturday.

Last weekend a grass-roots "Kony 2012 Cover the Night" campaign encouraged an international display of posters, stickers and murals calling attention to Joseph Kony, leader of a Ugandan guerrilla group accused of abducting children and forcing them to become sex slaves and child soldiers. He has been indicted for war crimes but remains at large. A film about his activities, "Invisible Children," became a YouTube sensation this spring.

"I think that it's super-disrespectful to deface someone's art," said Kpissay, who has participated in Walker programs. When he learned of the vandalism, he went to the Walker to apologize Sunday even though his group had nothing to do with it, he said.

Elsewhere, turnout for the "Cover the Night" campaign was minimal and the effort "flopped in trying to turn that [Internet sensation] into real-world actions," Britain's Guardian reported.

The Walker did not receive any Kony-related protest information, French said. "It could just be someone who was riding along with the activities elsewhere in the city. We're leaving it up to the police to discover."

French said the Walker is evaluating its security options. "We think we have a good system with the Minneapolis Park Police and the Minneapolis Police Department, but we're certainly looking into whether there are other things we could do to make things safer.

"I'm shocked that people would deface such a beloved object," he added. "Fortunately, we have a great crew and are really happy that it's cleaning up so well."